Tegra doesn't have irq_to_gpio() any more, and ak8975 is included integra_defconfig. This causes a build failure. Solve this with a heavy-handedmethod for now.

I suspect the long-term solution is to pass both the IRQ and GPIO IDsto the driver; the GPIO ID coming from either platform data, or perhapsenhancing struct i2c_client to add a gpio field alongside irq.